An untethered C3v-symmetric triarylphosphine oxide locked by intermolecular hydrogen bonding

A C_3v-symmetric triarylphosphine oxide locked into conformation by H-bonding and displaying an extended MOF-like solid-state structure is reported.

Probing Hydrogen Atom Transfer at a Phosphorus(V) Oxide Bond Using a "Bulky Hydrogen Atom" Surrogate: Analogies to PCET

Recent computational studies suggest that the phosphate support in the commercial vanadium phosphate oxide (VPO) catalyst may play a critical role in initiating butane C-H bond activation through a mechanism termed reduction-coupled oxo activation (ROA) similar to proton-coupled electron transfer (PCET); however, no experimental evidence exists to support this mechanism. Herein, we present molecular model compounds, (Ph₂N)₃V═N-P(O)Ar₂ (Ar = C₆F₅ (2a), Ph (2b)), which are reactive to both weak H atom donors and a Me₃Si^• (a "bulky hydrogen atom" surrogate) donor, 1,4-bis(trimethylsilyl)pyrazine. While the former reaction led to product decomposition, the latter resulted in the isolation of the reduced, silylated complexes (Ph₂N)₃V-N═P(OSiMe₃)Ar₂ (3a/b). Detailed analyses of possible reaction pathways, involving the isolation and full characterization of potential stepwise square-scheme intermediates, as well as the determination of minimum experimentally and computationally derived thermochemical values, are described. We find that stepwise electron transfer (ET) + silylium transfer (ST) or concerted EST mechanisms are most likely. This study provides the first experimental evidence supporting a ROA mechanism and may inform future studies in homogeneous or heterogeneous C-H activation chemistry, as well as open up a possible new avenue for main group/transition metal cooperative redox reactivity.

A Mono-, Di-, and Trivanadocene Phosphorus Oxide Series: Synthesis, Magnetism, and Chemical/Electrochemical Properties

In this Article, we outline the synthesis of B(C₆F₅)₃-coordinated mono-, di-, and trivanadocene phosphorus oxide complexes, Cp₂VOP(OB(C₆F₅)₃)Ph₂ (2), (Cp₂VO)₂P(OB(C₆F₅)₃)Ph (3), and (Cp₂VO)₃P(OB(C₆F₅)₃) (4), respectively (Cp = η⁵-cyclopentadienyl). The complexes were synthesized from the known reagents, Cp₂VF and Ph₂P(O)OSiMe₃ (for 2) or PhP(O)(OSiMe₃)₂ (for 3) or (Me₃SiO)₃PO (for 4), via Me₃SiF elimination and in the presence of B(C₆F₅)₃. The multimetallic complexes (3 and 4) could not be synthesized without the capping B(C₆F₅)₃ Lewis acid, whereas the uncapped version of 2, Cp₂VOP(O)Ph₂ (1), has previously been reported by us. Spectroscopic and crystallographic analyses of 2-4 support an increasingly Lewis basic P═O bond upon substitution of -Ph for -OVCp₂ fragments (2-4). The increased metal nuclearity also results in increasingly reducing complexes as evidenced by cyclic voltammetry (CV). Magnetic measurements (SQUID) further revealed high-spin complexes with negligible magnetic exchange between V centers. Chemical oxidation of 2 with 0.5 equiv of [Ag][B(C₆F₅)₄] resulted in a ligand rearrangement reaction producing the V^IV product, Cp₂V(OP(OB(C₆F₅)₃)Ph₂)₂ (7). In contrast, the oxidation of 4 with the trityl salt, [Ph₃C][B(C₆F₅)₄], resulted in the isolation of a mixed-valent V^III/V^IV dimetallic species, (Cp₂VO₂P(OB(C₆F₅)₃)OVCp₂ (9). Both oxidations likely produce the [Cp₂V][B(C₆F₅)₄] byproduct and evidence for its formation is presented. The synthesis and characterization of the mono- and dimetallic species, Cp₂VOP(OBPh₃)Ph₂ (8) and (Cp₂VO)₂P(OB(C₆F₅)₃)OSiMe₃ (5), is also reported.